Counter

I have a page with a registration form on it, when click submit, it sends me to a thank you page where I have the choice of paying with paypal or click a button to add another person. If I click "add another member" I go back to my first page.What I'd like, it's to have a counter to count how many times I went back and add a member so when I am ready to check out and pay it will show me the right amount.Do you know any simple script which can do that?Thank you.